Wednesday's two-hour finale (8 p.m., ABC 33/40) marks the end of this short but satisfying 16-hour season (one of its critical best) and opens the door to its sixth and final year.

One of the greatest things about ABC's mythology-dense, sci-fi drama is its insistence that fans pay attention and use their noodles each week. Critical thinking and a good memory add to the experience, keeps viewers on their toes and only makes each solved mystery more rewarding.

With that in mind, here are five things to consider when taking in season five's finale.

1: WHAT'S IN A NAME?
The season finale is titled "The Incident."

This event won't be lost on fans of "Lost." It was first referenced by Dr. Marvin Candle (aka Dr. Pierre Chang) in the Dharma Initiative's Swan Station training video discovered in season two by John Locke and Co. in the year 2004.

The 1980 reel explains, vaguely, the necessity for the button-pushing protocol of 4, 8, 15, 16, 23, 42 fame: "Not long after the experiments began (at the station), however, there was . . . an incident . . . and since that time, the following protocol has been observed . . ."

Fast forward (or rewind, rather) to April 29's "The Variable," set in 1977 where brilliant scientist and future man Daniel Faraday returns to the island after spending a couple years stateside at Dharma headquarters in Ann Arbor, Mich., presumably doing research and conducting experiments. Faraday predicts this incident with amazing accuracy. In fact, he has only a matter of hours to put things in motion that he hopes will ultimately save lives.

The plan: evacuate the island of all Dharma personnel, dig up the hydrogen bomb abandoned by the U.S. military and buried by the Others in the 1950s and detonate the warhead at the Swan Station site to contain a catastrophic pocket of electromagnetic energy, thereby changing history's timeline for the better.

2: WALK LIKE AN EGYPTIAN
We've seen so much ancient Egyptian culture, you'd think the empire might have extended to Dharma Island. Evidence:

1.) Hieroglyphics hide behind the Swan Station countdown clock and translate "underworld," according to producers. They also adorn the walls of the temple's chambers and Ben Linus' hidden door leading to the Smokey hot line. And don't forget that lesson on the Dharma schoolhouse chalkboard.

2.) Turn that frozen donkey wheel in the chamber beneath the Orchid Station, and you're teleported to the Tunisian desert. (That's close to Egypt.)

3.) John Locke and Co. got a glimpse of the ancient statue of which we've previously only seen a four-toed foot. The statue was holding an ankh -- or Egyptian cross -- to its side, which is typically carried by the loop by Egyptian gods. Dharman Paul was also wearing one of those ankhs when he was assassinated by the Others.

So what's with the cryptic question from newcomers: "What lies in the shadow of the statue?" It's likely something Egyptian, and we'll probably find out by season's end. Another important question: Why do Dharma and the Others seem to have folded elements of the same ancient culture into their own?

3: TIME TRAVEL
Castaways have gone from the 21st century to the 1950s to the '70s and beyond -- way beyond. This is the time travel season of "Lost."

While talk of constants, variables, paradoxes, fate and destiny can be overwhelming at times, the series' take on the staple sci-fi plot device isn't that hard to grasp.

While the writers had fans believe time and history were linear (constant and unchangeable), the show now seems to relax the rules on its version of time sliding.

This amendment, and the opportunity to set right a broken history, seems to be the driving force behind Jack Shepherd's return to hero status. It also sets up the season finale as a do-or-die situation for the time travelers.

If Jack and Co. is successful in its mission, three years of misery could be erased. If they fail, the castaways could die on the island. Or maybe -- and more likely -- the unkown will happen.

What does all this really mean for our time-traveling castaways? Possibly very little. A popular theory is they will vacate 1977 at season's end. The question is, though, where do they go from there? Will they return to their proper time or travel deeper into the past?

4: SOMEBODY DIES
It's "Lost." People die. The mortality of its players helps the series keep its edge because true life-and-death situations in this drama tell us something important is at stake.

When it happened to Charlie Pace, we were prepared. But knowing the screw-up-turned-hero was going to drown in a flooded Looking Glass Station didn't soften the event's emotional impact.

Daniel Faraday was just killed by his own mother (in the past) in an emotional turn.

And in Wednesday's episode, it's been rumored that another will die -- possibly an original cast member. (One series regular has been rumored to be pilot shopping. Another has been cast in a high-profile pilot for the next fall season, but the role isn't characterized as a series regular.)

What this means for those left behind and where the story is headed in the final season is any fan's guess, but like Charlie's departure, it's sure to resonate through the rest of the series.

And while "dead is dead" on "Lost," it doesn't mean a guest appearance as an island phantom or in a flashback/forward is out of the question.

5: AND INTRODUCING ...
(Spoiler alert)

The much-referenced head honcho of the Others and possible puppet master of the series' entire mythology, Jacob, is rumored to finally make an appearance along with some other familiar though yet-to-appear-in-person individuals.

Jacob's true role in the Others' end game has been a mystery for years. Fan speculation has cast him from simply a man in front of the curtain (a fictitious boogeyman the Others evoke to keep their comrades in line) to an alias for a future (or past) version of Ben Linus or John Locke. Neither possibility seems likely, as "Dexter's" Mark Pellegrino is rumored to be the cabin dweller in the finale.

Might the architects of the Dharma Initiative, including Dr. Alvar Hanso himself, finally be revealed, too? At this point it's anyone's guess who else might turn up, but Jacob's materialization is said to happen off-island, and executive producers promise Pellegrino won't be what everyone's talking about the next morning.

Does that foreshadow a game-changing plot twist setting up the final leg of "Lost"? Fans will have to wait until 2010 to find out.

ON THE HIATUS
OK, "Lost" won't be back for seven or eight months. Don't panic. Here's what you can do to keep the obsession going:

>> Catch up on or rewatch the first four seasons on DVD.>> Or just read. Here are a few books the Others have been caught reading on (and off) the island:

THE SEASON FINALE POLL
Question: What "Lost" mystery do you most want solved in the season five finale?

THE RESULTS>> Richard Alpert: Egyptian god, island phantom or something else? 31.7%>> What lies in the shadow of the statue? 18.8%>> Who's doing all that whispering in the jungles? 9.1%>> Who's this Jacob fellow? 44.1%>> What are the identities of the Adam and Eve skeletal remains in the caves? 15.1%